Wake on Lan

Wake-on-LAN, or WOL, is a feature available on almost all newer computers. The Wake-on-LAN feature can work in one of two ways. It can boot your system from a completely shutdown state if your the target machione supports the feature, or it can Wake-up your system from a hibernated (Windows) or sleeping state (Mac). The feature can also be used to wake up your computer while away from your home. A free software version of the client is available here for download.

The Magic Packet

The WoL protocol utilizes a “magic packet” to wake up the target machine. The "sleeping" target machine listens for the packet and responds to the packet when it arrives. These magic packets are sent over the entire LAN.

Support for WoL is pretty universal, even if it’s not advertised as a feature. Newer, more modern computers, now also have advanced BIOS options for allowing the computer to power on via a time schedule. While not the same, it provides an alternative.

Packet Structure of the Magic Packet

The data portion of the magic packet consists of a broadcast flag (FF FF FF FF FF) and the Mac address of the target machine repeated 16 times, then 6 bytes of 0s.